The build runner needs groups of jobs it can safely start together. Finish the planner so it respects dependency order and reports a cycle instead of producing a partial schedule that looks valid.
Build the implementation in Go under /app, with /app/run.sh as its entry point. Read one JSON request from standard input and write one JSON result to standard output. Input maps artifact names to direct dependency names. Return waves of sorted names; each wave contains every unbuilt artifact whose dependencies finished in earlier waves. Repeated dependencies count once. Reject unknown dependencies and cycles.
Reject inputs that violate an explicit validation rule with exit status 2, no standard output, and {"error":"invalid_input"} on standard error. For valid input, exit with status 0. Keep the implementation reusable for new inputs; it must work offline and must not depend on the example data being the only data it receives.
Repair or replace the unfinished /app/run.sh and add source files under /app. Malformed JSON must use the same invalid-input response. Do not read /tests or /oracle from the application.